Investigations on gas trapping phenomena for different EOR-water alternate gas injection methodologies

Water Alternate Gas (WAG) injection methods are the derivative of gas injection methods, wherein water and gas are injected intermittently. WAG injection can lead to improved oil recovery by combining better mobility control and contacting upswept zones and by leading to improved microscopic displacement. Gas trapping in the reservoir after WAG process is an important parameter that affects the recovery of oil. Trapped gas refers to the immobile gas saturation remaining after the rock is flooded with oil or water. Trapped gas creates significant hysteresis effect (during drainage and imbibition) and reduces the relative permeability of water in the mixed wet or oil wet reservoirs. In this work, gas trapping phenomena is presented for different WAG methods for a Indian Brownfield, namely, single, five cycle WAG, tapered WAG, five cycle WAG with Hydrocarbon gas (HC) and CO2 gas. Experiments are carried out on the recombined fluid in the core flooding apparatus at the reservoir conditions. The crude oil and gas is obtained from the separator at separator conditions and recombined at the reservoir conditions of 120oC and 230 kg/cm2 at reservoir gas-oil ratio (GOR) to become representative of the reservoir fluid. The actual core sample is obtained from the field and is used for the study. The water and gas injection rate used for this study are 20 and 10 cc/hr, respectively, for all the experimental studies. Two types of gases are used for WAG method, namely, hydrocarbon gas (collected from the field and having about 90 % methane by composition in mole %) and CO2 gas. The results on the saturation of phases and Land's trapping constant have been calculated for several cases of production life cycle and for different WAG methods.